1. Field of the Invention
This invention relates to transducing devices, and more particularly, to a composite mode transducer and a cooling device having the composite mode transducer.
2. Description of Related Art
A cooling system has come to the market for many years. In general, a device in motion generates heat. Such the heat makes a great impact on the operation of elements of the device. In a mechanical process such as a drilling process or a lathe cutting process, tools such as a cutting knife are easily expanded due to heat resulted from friction. In result, the size of the expanded cutting knife is changed, and the cutting knife cannot cut an element accurately. In order to ensure the cutting knife can cut the element accurately all the time, cutting fluid have to be applied to a cutting region, to dissipate the heat to a region from the cutting region. Similarly, the heat also makes a great impact on electronic components of an electronic device. Therefore, a cooling system for dissipating the heat to another region is not only necessary for the mechanical process, but is also crucial for a computer system, which comprises a plurality of electronic elements.
When the computer system is in operation, a central processing unit (CPU) or a graphics processing unit (GPU) of the computer system generates heat. In order to ensure that the computer system is operating within a specification temperature range required by a computer system manufacturer, the heat generated by the CPU or the GPU has to be dissipated to a region outside of the computer system as efficiently as possible. An air cooling mechanism including a fan and a heat-sink thermal module is one of the most popular air cooling systems in the art. In operation, the heat sink base of the thermal module are installed in contact with a heat source of an electronic device for conducting heat generated by the heat source to the heat-sink, and the fan exchanges cool air in a region outside of heat-sink with hot air in another region inside of the heat-sink, so as to reduce the temperature of an environment in which the electronic device is operating. A liquid cooling mechanism having cooling liquid is another one of the most popular cooling systems in the art. The liquid cooling mechanism takes the use of a closed-loop system to directly or indirectly contact and exchange heat with the heat source by circulating the cooling liquid.
The air cooling mechanism is still efficient enough to dissipate heat generated by a CPU, if the CPU is not operating at too high frequency. However, every 18 months a new generation CPU will come to the market, the new generation CPU having, according to Moore's law, double the number of transistors that an old generation CPU has. The new generation CPU runs much faster than the old one, and generates much more heat accordingly. The liquid cooling mechanism, which has a heat-dissipating efficiency better than that of the air cooling mechanism, is therefore widely applied to an electronic device having the new generation CPU in recent years. In early days, the air cooling mechanism dominates the cooling system market. Taiwan Patent No. 1235,907 discloses an air cooling mechanism, which operates in accordance with a temperature detecting circuit and a control circuit. As the CPU runs faster and faster and has a smaller die size, the CPU power density will increase and heat dissipation may become a problem.
According to the description of Taiwan Publication No. 200534776, cooling liquid is first guided to flow into a heat absorber to exchange heat with the heat absorber. Then the cooling liquid is pumped by a circulation pump to flow into a heat condenser to exchange itself with air in the heat-dissipating pipe. Taiwan Patent No. 451,045 also discloses a similar liquid cooling mechanism, which takes the use of an indoor heat exchanger to exchange waste heat with an outdoor air and a mist formed by vibrating the cooling liquid, to increasing the area on which a heat-exchanging process is performed and improve the performance of a heat-exchanging process.
Since the above-mentioned cooling mechanisms are still not efficient enough to dissipate the heat generated by the CPU, U.S. Pat. No. 6,713,942 B2, and Japan Patent No. 2002134975 and 200264599 as well, discloses a piezoelectric fan having a plurality of piezoelectric components. The piezoelectric fan is used for cooling heat-generating components, all of which have compact sizes and high power density, of a portable device, such as a notebook computer, a cellular phone or a digital camera. Similarly, Japan Patent No. 200261173 also discloses a cooling mechanism, which controls vibration boards of a piezoelectric fan to vibrate, so as to spray the cooling liquid onto the heat-dissipating components and cool the heat-dissipating components in result. A modern cooling system composed of a piezoelectric transducing device has a plurality of advantages, such as a compact volume, a simplified structure and a low power consumption, and has been widely applied to a variety of arts such as a computer system. For example, U.S. Pat. No 6,247,525 B1, as shown in FIG. 1, discloses that a driver 16 drives through a plurality of wires 14 a piezoelectric actuator 13 adhered to a bottom surface 12 of a diaphragm 15 to generate an ultrasonic vibration for atomizing mobile liquid droplets 19 flew from a fluid injection region 17 via a dispenser 18. The atomized liquid droplets 19 exchange heat with a heat-generating surface, and are cooled and condensed by a plurality of heat-dissipating fins and flow along a pipe back to an oscillation region, for a next action.
However, the piezoelectric actuator 13 is generally operating at a resonance frequency, and has a higher vibration power due to an influence of a resonance mode, so the piezoelectric actuator 13 has a greater atomized volume and a better heat-dissipating efficiency. Accordingly, when the piezoelectric actuator 13 is operating at the resonance frequency, components of the piezoelectric actuator 13 have lower resistances, and the piezoelectric actuator 13 has a larger electro-mechanical energy conversion ratio and can generate a larger atomized volume. However, the resonance frequency of the piezoelectric actuator is easily influenced by an environment such as a temperature, the variation of a boundary condition, or a package manufacturing process, so the resonance frequency has a problem for selection of fixed points, which is closely related to the performance of an atomization process. Moreover, the interference due to the diversity of moving directions of the piezoelectric actuators, which are all adhered to a single diaphragm, cause stress forces to be converged in a certain region of the diaphragm, and reduces durability, stability and working efficiency of the system. Furthermore, the resonance frequencies having thickness directions of the single piezoelectric actuator are located sparsely, so it is hard to design a control circuit and utilize their resonance characteristics, reducing the system usability.
Therefore, it is becoming one of the most important errands in the art to solve the above-mentioned problems and develop a transducing device and a cooling device having the transducer, so as to provide resonance frequencies closer in the thickness direction, simplify the design and increase the controllability of the system, prevent the convergence of stress forces and improve the durability by adjusting the particle sizes of the atomized liquid droplets in accordance with the variation of temperature, improve the heat dissipating efficiency, and prevent any environment factor from affecting the heat exchanging efficiency.